A conventional loudspeaker, or “speaker”, as used herein, may use a moveable diaphragm, or “speaker cone” to produce sound. Some speaker cones have radially symmetrical curvature, but may have shape variations (some are almost flat) that vary the geometry of the diaphragm from a strict geometric cone. The speaker cone is moved by a former, which also supports the voice coil. The former is attached to the speaker cone. The voice coil, which rests in the magnetic field of a magnet assembly, receives an audio-encoded electrical signal, or “audio signal”, which causes varying current in the voice coil. By interaction of the voice coil current with the magnetic field of the magnet assembly, sound-producing movement of the former and speaker cone results. The voice coil is constrained to one-dimensional motion, perpendicular to the base plane of the speaker cone, by a flexible support structure called a “spider.” The magnet assembly may comprise a magnetically permeable pole piece, a permanent magnet, and a magnetically permeable top plate. The pole piece may feature an annular groove, or “air gap,” to permit motion of the voice coil deeper into the magnetic field of the magnet assembly. The speaker cone is supported at its widest perimeter by a flexible suspension, or “surround”, which, in turn, is supported by a structure called a “basket.” The top plate of the magnet assembly and the spider are also connected to the basket. An opening in the speaker cone at its center may be covered with a dust cap, which reduces the amount of dust that may affect voice coil motion in the annular groove. At least a portion of the surround conventionally has a semi-circular or sinusoidal transverse cross-section.
Square speakers, as the term is commercially used, fall into two categories. First, there are speakers that have square portions of the basket, especially the rim of the basket, and have round, usually circular, diaphragms and surrounds (U.S. Pat. No. 2,998,496 issued to Hassan on Aug. 29, 1961). Second, and of primary interest here, are square speakers that have square diaphragms and square surrounds, each with rounded corners. Hereinafter, the terms “square speaker,” “square woofer” and the like, shall refer to speakers with square diaphragms and square surrounds, each with rounded corners. The advantage of a square speaker is that it may use the front area of a generally square or rectangular speaker cabinet with the greatest efficiency. Square speakers may produce more sound for a given area of cabinet front because the square diaphragm may take up more of the frontal area for a given size speaker. Additionally, square speakers may be arranged together with a minimum of wasted (non-diaphragm) space. Square speakers have been known for many years (U.S. Pat. No. 3,026,958 issued to Haerther, Jr. Mar. 27, 1962). The size of a square speaker is measured from side to side, just as with a round speaker.
The amount of sound produced by a speaker is proportional to the air volume displaced by the diaphragm in its axially oscillatory motion. The volume displacement, in turn, is determined as a function of the area of the plane of the diaphragm at its largest point and by the maximum distance it can travel from a quiescent state, called the speaker's “excursion.” The designer must strike a balance between the size of the surround, enabling larger excursions if the surround is larger, and the area of the diaphragm, which gets smaller as the surround gets larger, for a given speaker size. A further difficulty with a larger surround is that, in motion, the surround also pushes air and, therefore, makes sound. Because the surround is constantly changing shape as the diaphragm moves, the sound produced by the surround is of lower quality than that created by the rigid diaphragm. Accordingly, the aim of speaker design is to find ways to maximize volume displacement while maintaining high sound quality.
For square speakers, attaining a larger diaphragm area with a highly flexible surround is complicated by the corner areas of the surround. If the surround is of uniform cross-sectional shape, the material of the surround deforms in non-uniform ways at the corners during use. The non-uniform deformation may cause unwanted loads on the diaphragm that degrade sound quality, may require a stronger (heavier) diaphragm and so may require more work to move it, or may introduce a side force that causes binding between the former and the pole piece.
On Aug. 26, 2003 Irby, et al. were awarded U.S. Pat. No. 6,611,604 (hereinafter “Irby”) for an Ultra Low Frequency Transducer and Loudspeaker Comprising Same which disclosed pleats in the corners of a the surround of a square subwoofer. Irby's pleats are circumferential over the arch of the surround. Speakers manufactured similar to Irby are sold under the trade name KICKER. A particular ten-inch KICKER has a diaphragm area of 68 square inches and an excursion of one inch. Such a speaker has a ratio of volume displacement to speaker size of 13.6. Another particular twelve-inch KICKER has a diaphragm area of 100 square inches and an excursion of one inch. Such a speaker has a ratio of volume displacement to speaker size of 16.7.
The inventors have recognized a need for a square speaker with a larger displacement volume achieved at no loss to sound quality. The inventors have also recognized a need for a square speaker with higher ratios of volume displacement to speaker size (louder speakers). In order to meet those needs, and to solve related problems, the inventors have developed the novel square speaker of the present invention.